1. Field of the Invention
This invention relates generally to metal hardness testing and specifically to digital readout of Brinell specimen indentation diameter metal hardness test results when a Brinell penetrator has been applied to a test specimen using preselected force according to Brinell specimen indentation diameter test criteria.
2. Description of the Prior Art
Specimen indentation diameter testing, most commonly referred to as Brinell hardness testing, has long been known as one of the two principal means of testing the hardness of metals, the other well-known means being the specimen indentation depth test. In such Brinell hardness testing, a penetrator is applied to a test specimen, where the penetrator is a generally blunt probe, applied according to a predetermined load. The probe produces an indentation in the test specimen, with the diameter of the indentation, when related to the force with which the penetrator is applied, defining Brinell hardness of the test specimen. Typically, diameter of the indentation is measured along two axes, perpendicularly disposed respecting one another. (This is because many times the indentation actually is an ellipse, as opposed to a circle.) The two diameters, referred to as major and minor diameters, are averaged to produce a diameter of a circle, which is used to compute Brinell hardness of the test specimen.
Such Brinell hardness testing is favored over penetration testing because such Brinell tests are generally recognized as more accurate than penetration tests. This is because Brinell tests involve a greater area of the test specimen and apply a higher load to the area. Because more area is involved, greater accuracy of the test reading is inherent.
Heretofore, indentation depth testing has been the only high-speed, high production type of testing. This is because heretofore, there has not been means or methods for accurately and quickly measuring the diameter of the impression produced utilizing the Brinell technique. Because penetration depth can be relatively easily and relatively quickly measured, indentation depth testing has been the only high speed, high production metal hardness testing heretofore.
To solve the long-standing problem of accurately and automatically measuring diameter of a Brinell hardness indentation, artisans have utilized small video cameras to obtain a picture of the indentation and computers to digitally resolve the indentation picture, to derive the indentation diameter, which is the classic representation of Brinell hardness.
To date, results have been disappointing, principally because of poor edge definition of the detected indentation. Light sources used heretofore have not adequately illuminated the edge and have not provided adequate definition of the edge structure relative to surrounding area. Known equipment employs a video camera directly over the indentation, having a lens system looking straight down into the indentation. Typically, a light source is placed next to the camera to produce an angle of incidence of the applied light beam, relative to the indentation and the surrounding area, which is nearly perpendicular to the indentation bottom and nearly perpendicular to the plane of the test specimen surface surrounding the indentation.
In such systems, the light emitted by the light source strikes the indented area and the area surrounding the indentation; the light is reflected from both the indentation and the surrounding area with approximately the same intensity and the same amount of scattering. If the surface of the test specimen surrounding the indentation has structure similar to the portion of the test specimen which has been indented (which is frequently the case in industrial applications, where the test specimen may be unpolished or have a rough surface in the test area) light reflections back to the camera from the indentation and the surrounding area produce a low resolution image of the indentation edge, or perhaps no image of the edge at all.
Patent prior art known to applicants consists of U.S. Pat. Nos. 1,209,350, 1,232,782, 1,384,389, 1,646,195, 1,770,045, 1,973,333, 2,319,208, 2,418,916, 2,448,486, 2,466, 567, 2 535,830, 2,643,544, 2.693,698, 2,804,769. 2,835,127, 2,976,723, 3,102,417, 3,128,621, 3,138,951. 3.295,363, 3,478,568, 3,486,373, 3,728,551, 3,754,436, 3,815,125, 3,822,946, 4,036,048, 4,075,478, 4,094,188, 4,147,052, 4,193,199, 4,312,220, 4,372,152 D 178,060, D 228,174, and D 283,599; Japanese patent publications Nos. 51-94,884 and 52-155,588; German patent publications Nos. 2,357,755 and 2,751,095; and Russian Pat. No. 358,648. Of these, U.S. Pat. Nos. 3,822,946 and 4,372,152 are believed to be the most relevant.
Non-patent printed prior art known to applicants includes the publication Introdyne Universal Horizontal Hardness Tester, published by Blue River Laboratories, RD #4, Box 76, Lewistown, Pa. 17044; Hirth Mini Meter for Accurate Measuring published by Falkimer Machinery Company, Ltd., Famacoy House, Goulburn Street, Sydney, Australia and a brochure entitled Foundrax Brinscan supplied by Foundrax Corporation in Great Britain.